Implement Stack using Queues

最新推荐文章于 2023-03-22 04:55:35 发布

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本文介绍了一种使用队列来模拟栈操作的方法，包括push、pop、top和empty等基本操作。通过不断将队首元素出队再入队的方式，使得最新加入的元素始终位于队首，从而模拟栈的特性。

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mplement the following operations of a stack using queues.

push(x) – Push element x onto stack.
pop() – Removes the element on top of the stack.
top() – Get the top element.
empty() – Return whether the stack is empty.
Notes:
You must use only standard operations of a queue – which means only push to back, peek/pop from front, size, and is empty operations are valid.
Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).

方法：队列实现栈，注意将数字压入到队列中时需要循环出队进队模拟栈，效率不高。

class MyStack {
private:
    queue<int> q;
public:
    /** Initialize your data structure here. */
    MyStack() {

    }

    /** Push element x onto stack. */
    void push(int x) {
        q.push(x);
        for(int i = 0 ; i < q.size() - 1; ++i){
            q.push(q.front());
            q.pop();
        }
    }

    /** Removes the element on top of the stack and returns that element. */
    int pop() {
        int res = q.front();
        q.pop();
        return res;

    }

    /** Get the top element. */
    int top() {
        return q.front(); 
    }

    /** Returns whether the stack is empty. */
    bool empty() {
        return q.empty();
    }
};

/**
 * Your MyStack object will be instantiated and called as such:
 * MyStack obj = new MyStack();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 = obj.top();
 * bool param_4 = obj.empty();
 */